[156] Check whether there exist objects without any context

One implicit constraint is that all objects within the model should be
connected transitively to the StartEvent. The only exception to this
constraint are objects of type 'Comment', 'Exception' or 'Constraint'.

This adaption of the evaluation script compares the number of objects
within the whole model (objects of the types mentioned above are not
taken into consideration) to the number of objects transitively
connected to the StartEvent including the StartEvent.
Merge branch 'feature-156' into develop